“Last week I informed the Convener of the Scottish Liberal Democrats that I intended to stand down as Party Leader.
“Today I am formally announcing that decision, with immediate effect.
“Everyone involved in politics knows that there are stresses and strains on family life.
“But when it goes beyond that, when it crosses a line, something has to be done.
“And at that stage - when you have to make a choice between family and politics - there can only be one answer. The health and wellbeing of your family has got to come first.
“With four children between the ages of 4 and 12, my family has got to be my priority.
“As an MSP representing a constituency well away from Edinburgh, I have been away from home at least four working days each week for more than nine years.
“As a Party Leader the responsibilities have been even more demanding. You have to be available every day, every week. There is rarely a weekend, a birthday or a family holiday when the demands of the job do not intrude.
“That is not to complain – long hours and long absences from home go with the job.
“But it can all have an impact.
“And when that impact becomes too great, it is time to put my family first.
“I will continue to represent Aberdeen South in the Scottish Parliament. I intend to remain a strong campaigner on behalf of my city and my constituents.
“It has been an honour and a great privilege to lead the party over the last three years and to be part of the first generation of Liberal Democrats to be in government in Britain since the Second World War.
“In that time the Scottish Liberal Democrats have achieved much for the people of Scotland. We succeeded in scrapping student tuition fees, in setting bold targets for renewable energy and in delivering a fair voting system for local government.
“As a Minister, I welcomed the chance to deliver the Parliament’s first cut in business rates, to introduce enterprise education for every child and to kick start new wave and tidal projects to release Scotland’s potential to be the renewable energy powerhouse of Europe.
“And, during my time as leader, the Party shook the foundations of Scottish politics when Willie Rennie gained the Dunfermline and West Fife by-election from Labour. We also gained Dunfermline West at the Scottish election, and across Scotland saw our number of votes and our share of the vote increase – a notable achievement for a party which had been in power for eight years.
“Our party is united and our shadow cabinet team has been taking the fight to the SNP in Parliament with a strong and consistently effective performance.
“And I have enjoyed challenging the new First Minister at question time each week. I will miss that.
“I will miss it all, a great deal.
“My hunger for change in Scotland – tackling global warming, building the role of young people in our country and stopping the slide of civil liberties – is no less now than when I started in politics 25 years ago.
“However, that drive and that passion comes at a price. And it is a sacrifice that that my family should no longer have to make. Their happiness is more important than any political office and that is the reason for me standing down as leader of the Scottish Liberal Democrats.
“Our new leader can be assured of my total support and my constant encouragement. It has been a fascinating few days in Scottish politics and today’s announcement will be for most another unexpected twist.
“But the fundamentals are clear.
“The Liberal Democrats are united, strong and growing.
“Labour are coming to the end of their time at Westminster. The SNP are starting to find government tougher than they expected. Broken promises catch up with you. And the Conservative strategy of continually propping up the SNP in Holyrood remains to me simply staggering.
“I believe that there is a huge opportunity for our party at this time. It is going to be an exciting few years.
“And I wish my successor great success.
“Finally, I want to thank friends and colleagues for their support, advice and encouragement. They know who they are – at Westminster, at Holyrood and across Scotland. I will not get into that cliché of mentioning a long list of those who have meant so much to me over the years, but they know who they are.
“Above all, however, I want to thank my wife Caris and my four kids for all their help - and all they put up with - in supporting my life in politics.
“That other cliché is for a politician to say he is looking forward to spending more time with his family.
“In my case it happens to be true.
“Perhaps my announcement today should alert people to the demands which are placed on politicians and their families.
“For me, it is simpler than that. Recognising those demands, it reflects what I must do - as a personal, not a political, priority.